In this article we report on a historical study of the calendars and guides published by the Public Record Office (PRO) of Great Britain between 1838 and 1968. Drawing on rhetorical genre theory, we conceive of these finding aids as sociohistorical texts and trace their evolution across three dimensions (textual features, composing processes, and social roles). Our study suggests that the calendars and guides were not simply tools for making the PRO’s holdings accessible to the public; they also shaped and were shaped by ideas and beliefs about what it meant to make records accessible to the public and the most effective means of accomplishing that end. These ideas and beliefs were linked, in turn, to the PRO’s sense of its purpose and identity in relation to the communities it served. The generic evolution of the calendars and guides reflects and, to some extent, embodies that evolving sense of purpose and identity.